This application seeks support for the infrastructure of the Multiethnic Cohort (MEC) Study, which was established in Hawaii and southern California between 1993 and 1996 to study risk factors for cancer and other chronic diseases. The study was designed to take advantage of the ethnic and cultural diversity of the two geographic areas, as well as the expertise of the senior investigators in nutrition, ethnic/racial studies, and, subsequently, genetics. It is the most ethnically heterogeneous cancer cohort in existence. At baseline, the cohort included information on 215,000 men and women, comprised, by design, almost entirely of five ethnic/racial populations: Caucasians, Japanese Americans, Native Hawaiians, African Americans, and Latinos. The resource was later expanded to include a prospective bio repository of blood and urine specimens from ~ 70,000 of the participants. Leadership of the MEC entails a highly interactive, team approach; and the investigators have amply demonstrated their willingness to share data and participate actively in consortium projects. This application describes our aims over the next five years for maintaining and enhancing the infrastructure of the MEC, as well as plans for methodological research in the areas of genetic and nutritional epidemiology that utilize the resources of the cohort. Research accomplishments to date include significant contributions to understanding both genetic and environmental risk factors for cancer, particularly related to breast, prostate, colorectal and lun cancers. Nearly 250 papers describing these findings have been published. In addition, primarily over the last 20 years, more than 50 research grants have been built around the MEC, and more than 50 students and postdoctoral fellows have been trained on the study. This new grant will make possible the continuation of a well-integrated program of research aimed at evaluating environmental factors and genetic variants as risk factors for cancer and other common chronic diseases.